Keyboard scanning circuit

Abstract

A keyboard scanning circuit, comprising N wires, and [(2N−1)+(2N−1−1)N] switches divided into two switch groups, therein N is a natural number. Each switch includes a first contact and a second contact. The first contacts of the (2N−1) switches in the first switch group are connected to ground, the second contacts of the (2N−1) switches in the first switch group are connected to the wires in (2N−1) connectors. The first contacts of the (2N−1−1)N switches in the second switch group are connected to one of the wires, the second contacts of the (2N−1−1)N switches in the second switch group are connected to the nodes between the switch in the first switch group and the wires.

1. A keyboard scanning circuit, comprising:
 N wires; and 
 [(2 N −1)+(2 N−1 −1)N] switches divided into two switch groups; wherein N is a natural number, each switch includes a first contact and a second contact, the first contacts of the (2 N −1) switches in the first switch group are connected to ground, the second contacts of the (2 N −1) switches in the first switch group are connected to the wires in (2 N −1) connectors, the first contacts of the (2 N−1 −1)N switches in the second switch group are connected to one of the wires, the second contacts of the (2 N−1 −1)N switches in the second switch group are connected to the nodes between the switch in the first switch group and the wires. 
 
     
     
       2. The keyboard scanning circuit as claimed in  claim 1 , further comprising a plurality of diodes set between the first switch group and the wires to keep signals flowing in one direction. 
     
     
       3. The keyboard scanning circuit as claimed in  claim 2 , cathode of the diodes are connected to the wires, anode of the diodes are connected to switches in the first group. 
     
     
       4. The keyboard scanning circuit as claimed in  claim 1 , wherein each wire is I/O wire. 
     
     
       5. The keyboard scanning circuit as claimed in  claim 1 , wherein the switches in the first switch group are determined by setting the input ports of the N wires high, and scanning the output ports of the N wires. 
     
     
       6. The keyboard scanning circuit as claimed in  claim 1 , wherein the switches in the second switch group are determined by setting the input ports of the wires I/O 1 ˜I/O 3  sequentially low, and scanning the output ports of the N wires.